The present invention generally relates to the control of heat transfer apparatus and, in a preferred embodiment thereof, more particularly relates to control and calibration apparatus and methods for use in conjunction with fuel-fired air heating furnaces having modulatable fuel valves and supply air blowers.
In the design of fuel fired air heating furnaces that heat and deliver recirculating air to a conditioned space making variable heating demands on the furnace, two separate operational design challenges are typically presented--namely (1) the comfort of the occupants in the conditioned space served by the furnace, and (2) the operational stability of the various components of the furnace. From the comfort standpoint, for example, an air delivery temperature that is either too cool or too hot may be perceived by a conditioned space occupant as uncomfortable even though the changing heating demands of the conditioned space are, from a heat delivery perspective, being precisely met by the furnace. From the standpoint of furnace operational stability, it is desirable to avoid wide variations in, for example, the flow rate ratio of external supply air and internal combustion products traversing the heat exchanger portion of the furnace.
Yet in conventionally controlled furnaces it is typically difficult to satisfy each of these two operational design parameters--typically, an improvement in one tends to at least somewhat degrade the other. It is accordingly an object of the present invention to provide a fuel fired air heating furnace, and associated control system, that enables the furnace to provide both improved conditioned space occupant comfort levels, and enhanced operational stability for the furnace itself, compared to typical fuel fired air heating furnaces of conventional design.